Filtering pulley

ABSTRACT

A filtering pulley having a hub adapted to be fixed to a rotating shaft, a pulley ring mounted coaxial and rotationally free on the hub, and a plurality of elastic assemblies arranged circumferentially with respect to the hub and the pulley ring and each interposed between a pair of first elements integral with the hub and between a pair of second elements integral with the pulley ring is disclosed. Each elastic element forms with the first elements and with the second elements respective angular clearances, and the pulley ring and the hub have a free angle of relative rotation equal to the sum of the above-mentioned angular clearances.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is filed under 35 U.S.C. § 371 as the U.S.national phase of International Patent Application No.PCT/IB2016/051549, filed Mar. 18, 2016, which designated the UnitedStates and which claims the benefit of Italian Patent Application No.102015000009369, filed Mar. 20, 2015, each of which is herebyincorporated in their entirety including all tables, figures, andclaims.

TECHNICAL FIELD

The present invention concerns a filtering pulley, preferably a pulleyfor a crank shaft in an ancillaries transmission of an internalcombustion engine.

BACKGROUND ART

As is known, the drive shaft in internal combustion engines is subjectto torsional vibrations due to the periodic stress caused by thecombustion in the cylinders. These vibrations are particularly intenseat start-up and at low speeds, and in the presence of particularconstruction solutions such as dual-clutch transmissions or start-stopsystems.

The torsional vibrations translate into irregular rotations of theancillaries transmission drive pulley which are transmitted to theancillaries by means of the drive belt, which is therefore subject toperiodic tension variations.

In order to “filter” the torsional oscillations transmitted from thecrank shaft to the belt, a filtering pulley is generally used as drivepulley, provided with a hub integral with the drive shaft, a pulley ringcooperating with the belt and one or more elastic elements via which thedrive torque is transmitted from the hub to the pulley ring.

To effectively filter the oscillations, the rigidity of the elasticelements should be low; however, the high loads absorbed by theancillaries do not allow the rigidity to be lowered beyond a certainlimit. The need is therefore felt in the sector to develop improvedfiltering pulleys which meet the conflicting needs described above.

DISCLOSURE OF INVENTION

The object of the present invention is to provide a filtering pulleythat solves the above-mentioned technical problem in a simpleinexpensive manner.

The above-mentioned object is achieved by a filtering pulley accordingto claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, a preferredembodiment is described below, by way of non-limiting example and withreference to the accompanying drawings, in which:

FIG. 1 is a diametral section of a pulley according to the invention;

FIG. 2 is a perspective view of the pulley of FIG. 1 with parts removedfor clarity;

FIG. 3 is a front view of the pulley of FIG. 1 with parts removed forclarity;

FIGS. 4 and 5 are sections along the line IV-IV of FIG. 1 in respectiveoperating phases of the pulley;

FIG. 6 is an exploded perspective view of an elastic assembly accordingto a variation of the pulley of FIG. 1;

FIG. 7 is a perspective view of a damping element of the pulley subjectof FIG. 1;

FIG. 8 is a graph showing the damping torque provided by the element ofFIG. 7 according to the rotation angle of the pulley of FIG. 1;

FIGS. 9 and 10 are graphs showing the torque transmitted by the pulleyof FIG. 1 according to its angle of rotation, without and with dampingrespectively;

FIG. 11 is a transverse view of a further variation of the pulleysubject of the invention; and

FIG. 12 is a graph showing the torque transmitted by the pulley of FIG.11 according to its angle of rotation.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1 to 3 show a filtering pulley 1 comprising a hub 2 with axis Aadapted to be connected to a shaft (not shown), for example a crankshaft of an internal combustion engine, and an annular pulley ring 3externally coaxial to the hub 2 and supported in a rotationally freemanner on the hub 2 by means of a bearing 4, preferably a rollingbearing.

The pulley ring 3 comprises an annular portion 5 provided with a profile6 designed to cooperate with a poly-V belt (not shown). The pulley ring3 further comprises a radial wall 7, integral with the annular portion 5and preferably in one single piece with it, extending radially towardsthe hub 2 and an inner substantially cylindrical wall 8 with axis A.

The pulley ring 3 carries, integral with it, a closing element 11comprising an outer cylindrical wall 12 with axis A, a flat radialannular wall 13 and an inner cylindrical wall 14 with axis A, projectingfrom the wall 13 on the opposite side of the cylindrical wall 12. Theclosing element 11 is press-fitted into the pulley ring 3 so as to forman annular chamber 15 radially comprised between the wall 12 and thewall 8 and axially delimited by the wall 7 and the wall 13. Lastly, theclosing element 11 comprises two protrusions 16, 17 diametricallyopposite extending axially into the chamber 15 from the wall 13 and twoopenings 18 obtained in the wall 14 and positioned at a halfway point ofthe angular distance between the protrusions 16, 17.

The wall 7 of the pulley ring 3 forms corresponding protrusions (notillustrated) facing the protrusions 16,17 of the closing element 11.

The pulley 1 is further provided with a dynamic damper 19 comprising adisc 21, facing the closing element 11 and having a hub portion 22integral with the hub 2, and a seismic ring 23 secured to a perimeterflange 24 of the disc 21 by a ring 25 of elastomeric material.

The pulley 1 comprises a friction damper 27 radially interposed betweenthe wall 14 of the element 11 and the hub portion 22 of the disc 21 ofthe dynamic damper 19. The damper 27 substantially comprises a C-bushing28 which slidingly cooperates with a cylindrical surface obtained on thehub portion 22 and an open metallic ring 29 mounted with radial drivingon the bushing 28 and rotationally coupled to the same by means of apair of radial protrusions 30 which engage corresponding holes in thering 29 (FIG. 7).

The ring 29 comprises, at one of its ends, at least one outer radialprotrusion 31 housed with freedom of movement in the circumferentialdirection inside the opening 18.

The pulley 1 further comprises a plurality of, for example two, archedelastic assemblies 40 arranged circumferentially free in the respectiveportions 15 a, 15 b of the chamber 15 delimited by the protrusions 16and 17. The travel of the elastic assemblies 40 in the respectiveportions 15 a, 15 b is given by an angular clearance α present betweeneach of the elastic assemblies 40, arranged in contact with one of theprotrusions 16, 17 and the other protrusion 17, 16.

Each of the elastic assemblies 40 comprises a pair of arched helicalsprings 41,42, positioned in series with each other and mounted betweenrespective end sliding blocks 43 and an intermediate sliding block 44.The springs 41,42 have different rigidities, more precisely greater andlesser as will be described in further detail below. The sliding blocks43 each comprise an arched portion 45 which internally surrounds an endportion of the respective spring 41,42, and a head 46 defining an axialsupport for said end portion. The sliding block 44 comprises an archedportion 47 which internally surrounds respective opposite end portionsof the springs 41,42 and an intermediate radial partition 48 comprisedbetween the two springs 41,42.

Lastly, the pulley 1 comprises an actuator 49 interposed axially betweenthe hub 2 and the disc 21 of the dynamic damper 19 and integral withthem. The actuator 49 has two spokes 50 free to move circumferentiallyin the chamber 15 and adapted to interact with the elastic assemblies40. Assuming that the actuator 49 is arranged so that each of the spokes50 is angularly equispaced with respect to the elastic assemblies 40,the angle comprised between each of the spokes 50 and each of theelastic assemblies 40 will be equal to σ/2, where σ represents the totalangular clearance between the spokes 50 and the elastic assemblies 40.

The operation of the pulley 1 is described below with reference first tothe simplified graph of FIG. 9, which shows the torque transmitted bythe pulley 1 according to the relative angle of rotation between thepulley ring 3 and the hub 2, supposing for the sake of simplicity thatthe dampings are absent.

As can be seen from the graph, there is an angular interval β in whichthe hub 2 and the pulley ring 3 can rotate with respect to each otherwithout any transmission of torque. This angular interval, or freeangle, is equal to the sum of the angular clearances α and σ describedabove.

In a first operating phase, called driving mode and constituting thenormal operating mode of the pulley 1 when the drive shaft drives theancillaries, the speed of the hub 2 tends to exceed the speed of thepulley ring 3. Therefore the spokes 50 of the actuator 49, once the freeangle β has been overcome, consisting, as described above, of the sum ofthe angular clearance a between the spokes 50 and the elastic assemblies40 and of the angular movement a of the latter, transmit the torque tothe protrusions 16, 17 with interposition of the respective elasticassemblies 40.

As the torque transmitted increases, the elastic deformation of thesprings 41, 42 positioned in series with each other increases; therelation between torque and relative angle of rotation is thereforelinear, with a first gradient K1 defined by the equivalent rigidity ofthe two springs 41,42 in series.

When the spring 41 is fully compressed, the rigidity of the elasticassembly 40 is equal to that of the spring 42 and therefore greater, ascan be seen from the section with higher gradient K2 of the graph ofFIG. 9. When the spring 42 is also fully compressed, the elasticassembly 40 behaves like a rigid body, as can be seen from the verticalsection of the graph of FIG. 9.

What has been described for the driving mode occurs symmetrically in theoverrunning condition, in which the speed of the pulley ring 3 tends toexceed the speed of the hub 2.

The damper 27 acts between the hub 2 and the pulley ring 3, in parallelto the elastic assemblies 40; the effects are illustrated in the graphof FIG. 8. The damper 27 has an asymmetric behaviour between the drivingmode and the overrunning mode.

In particular, in the driving mode (FIG. 5), the ring 29 is arrangedwith the protrusion 31 in contact with the end 18 a of the opening 18facing in the direction of the rotation. The ring 29 is thereforeintegral with the pulley ring 3 and a sliding occurs between the bushing28 and the hub portion of the disc 18.

The contact force between the protrusion 31 and the end 18 a of theopening 18 determines a torque which tends to “open” the ring 29. Thisdetermines a relatively reduced damping value D1 but greater than avalue D0 equal to the damping that would be present in the absence ofthe damper 27, generated for example by the friction associated with theelastic assemblies 40. During this phase, the amplitude oscillations,which are less than the angular amplitude of the opening 18, causedetachment of the protrusion 31 from the end 18 a and are optimallyfiltered thanks to the low damping value D0.

When the torque between the driving mode and the overrunning mode isinverted, the ring 29 rotates with respect to the pulley ring 3 so thatthe protrusion 31 reaches the opposite end 18 b of the opening 18.During this rotation the damping value is equal to D0.

In the overrunning mode the protrusion 31, cooperating with the end 18b, produces a torque which tends to close the ring 29 on the hub portion22, thus causing a damping D2 with value greater than D1. Also in thiscase any amplitude oscillations less than the angular amplitude of theopening 18 cause detachment of the protrusion 31 from the end 18 b andare optimally filtered thanks to the low damping value D0.

FIG. 10 is analogous to FIG. 9 but takes account of the dampings; thecurve therefore shows a hysteresis generated by the damping describedabove.

FIG. 6 illustrates an embodiment variation of an elastic assembly 40,indicated as a whole by the number 52. The elastic assembly 52 comprisesone single spring 53 provided with a pair of end pads 54 which areadapted to cooperate with the spokes 50 and with the protrusions 16, 17.The elastic assembly 52 further comprises an anti-warping element 55 forthe spring 53, consisting essentially of an arched cylinder made ofpolymer material, coaxial to the spring 53 and housed with slightinterference inside the spring.

During the full compression of the spring 53 the anti-warping element 55does not allow overlapping of the coils of the spring 53.

FIG. 11 shows a second variation of the pulley 1 in which the elasticassemblies 40 consist of one single arched helical spring 60 which ispositioned around the circumference of the chamber 15 and whichcooperates with the protrusions 16 and 17 and the spokes 50.

The two variations described above allow the torque illustrated in FIG.12 to be obtained. Again, an angular interval β is present in which thehub 2 and the pulley ring 3 can rotate with respect to each otherwithout any transmission of torque; once said interval is exceeded,transmission of the torque begins along a line with unique gradient K3until the elastic assembly 52 or the spring 60 are fully compressed, asituation shown by the vertical section of the graph of FIG. 12.

The advantages of a pulley 1 according to the invention are thereforeevident. The use of elastic assemblies 40 with angular clearance α withrespect to the protrusions 16,17 and an actuator 49 with an angularclearance σ with respect to the elastic assemblies 40 allows a very highfree angle β to be obtained which permits decoupling of the hub 2 andpulley ring 3 in the presence of high amplitude torsional oscillations,such as those that occur at start-up, for example, thus avoidingsubjecting the belt and ancillaries to undesired impact loads.

Thanks to the presence of the free angle β, the springs 42 can bedesigned with a relatively high rigidity, optimal for transmission ofthe torque, even though the overall system comprising the elasticassemblies 40 and the angular clearances α and σ has a low equivalentrigidity.

The damper 27 is activated only for relative rotations greater than theamplitude of the opening 18 and therefore, for oscillations with loweramplitude, the filtering capacity of the pulley 1 is not affected. Inthe presence of large amplitude relative rotations, the damper 27behaves asymmetrically, with greater damping in the overrunning phase.

Lastly it is clear that modifications or variations can be made to thepulley 1 described that do not depart from the protective scope definedby the claims.

For example, with reference to the elastic assembly 40, the slidingblocks 43,44 and the anti-warping element 55 could be made differentlywithout modifying their function.

The dynamic damper 19 could be absent. Lastly, the opening 18 and theangular intervals α, σ could have different amplitude according to thedynamic torsional behaviour of the drive shaft in the specificapplication.

The invention claimed is:
 1. A filtering pulley comprising: a hubdefining a bore for receiving a shaft and an axis of rotation, a pulleyring mounted coaxial and rotationally free on said hub, a plurality ofelastic assemblies arranged circumferentially with respect to said huband said pulley ring and each interposed between a pair of firstelements integral with said hub and between a pair of second elementsintegral with said pulley ring, wherein each of the plurality of elasticassemblies forms with said pair of first elements and with said pair ofsecond elements respective angular clearances (σ, α), said pulley ringand said hub having a free angle (β) of relative rotation in which thehub and pulley ring rotate with respect to each other without anytransmission of torque, wherein the free angle (β) is equal to the sumof said angular clearances (σ, α); wherein said plurality of elasticassemblies comprise a first arched spring having two sliding blocksapplied to respective ends of said first arched spring, the first archedspring and the two sliding blocks slide circumferentially inside a seatformed by said pair of first elements and/or said pair of secondelements; wherein each of the two sliding blocks are elongate andcomprise an arched portion which surrounds a plurality of coils of saidfirst arched spring and a head perpendicular to said arched portionwhich receives an end of said first arched spring.
 2. A pulley accordingto claim 1, characterized in that said pair of first elements compriseat least two spokes carried by an actuator integral with the hub.
 3. Apulley according to claim 1, characterized in that said pair of secondelements are protrusions obtained on an element which is integral withthe pulley ring.
 4. A pulley according to claim 1, characterized in thatsaid plurality of elastic assemblies comprises a second arched spring inseries with said first arched spring.
 5. A pulley according to claim 4,characterized in that said first and second arched springs havedifferent rigidities.
 6. A pulley according to claim 4, characterized inthat said plurality of elastic assemblies comprises an anti-warpingdevice for each of said first and second arched springs.
 7. A pulleyaccording to claim 6, characterized in that said anti-warping devicecomprises a polymeric material element accommodated coaxial inside saidfirst and second arched springs.
 8. A pulley according to claim 1,comprising a damper configured so as to dampen the relative oscillationsbetween said hub and said pulley ring.
 9. A pulley according to claim 8,characterized in that said damper has an asymmetric damping.
 10. Apulley according to claim 8, characterized in that said damper comprisesa C-bushing which slidingly cooperates with a cylindrical surface whichis integral with one of said hub and said pulley ring and comprises anopen metallic ring mounted radially outward on said C-bushing andcoupled rotationally thereto, said open metallic ring comprising aprotrusion adapted to cooperate with an end of an opening of another ofsaid hub and said pulley ring.
 11. A pulley according to claim 10,further comprising a dynamic damper.
 12. A pulley according to claim 11,characterized in that the dynamic damper comprises a disc which isintegral with the hub and in that said cylindrical surface belongs tosaid disc.
 13. A filtering pulley comprising: a hub defining a bore forreceiving a shaft and an axis of rotation, a pulley ring mounted coaxialand rotationally free on said hub, a plurality of elastic assembliesarranged circumferentially with respect to said hub and said pulley ringand each interposed between a pair of first elements integral with saidhub and between a pair of second elements integral with said pulleyring, wherein each of the plurality of elastic assemblies forms withsaid pair of first elements and with said pair of second elementsrespective angular clearances (σ, α), said pulley ring and said hubhaving a free angle (β) of relative rotation in which the hub and pulleyring rotate with respect to each other without any transmission oftorque, wherein the free angle (β) is equal to the sum of said angularclearances (σ, α); and an asymmetric damper that dampens the relativeoscillations between said hub and said pulley ring, the asymmetricdamper comprising: a C-bushing which slidingly cooperates with acylindrical surface which is integral with one of said hub and saidpulley ring and comprises an open metallic ring mounted radially outwardon said C-bushing and coupled rotationally thereto, said open metallicring comprising a protrusion adapted to cooperate with an end of anopening of another of said hub and said pulley ring.
 14. The pulley ofclaim 13, further comprising a dynamic damper; wherein said dynamicdamper comprises a disc having a perimeter flange and a seismic ringsecured to said perimeter flange by a ring of elastomeric material. 15.The pulley of claim 14, wherein said dynamic damper is integral with thehub and defines said cylindrical surface with which the asymmetricdamper slidingly cooperates.
 16. The pulley of claim 13, wherein saidplurality of elastic assemblies comprises a first arched spring havingtwo sliding blocks applied to respective ends of said first archedspring, the first arch spring and two sliding blocks slidingcircumferentially inside a seat formed by said pair of first elementsand/or said pair of second elements; and wherein each of the two slidingblocks comprise an arched portion surrounding a side portion of saidfirst arched spring and a head perpendicular to said arched portion. 17.The pulley of claim 16, wherein said pair of first elements comprise atleast two spokes carried by an actuator integral with the hub.
 18. Thepulley of claim 16, wherein said pair of second elements are protrusionsobtained on an element which is integral with the pulley ring.
 19. Thepulley of claim 13, wherein said plurality of elastic assembliescomprises two arched springs in series with one another, and said twoarched springs have different rigidities.